In the turbomachinery field, gaskets are used to separate zones operating at different pressures. A gasket may be located between a tubular assembly, which may be a compressor bundle formed by one or more diaphragms and a rotor, and an outer casing.
In the prior art, at least an annular groove is provided on the tubular assembly outer surface to house a closed-ring gasket, usually realized in a Teflon (PTFE) based material. In order to fit the gasket in the annular grove, the first step is to heat-up the closed-ring gasket to temporary increase its diameter. The increase of the gasket diameter makes it possible to fit it onto the tubular assembly and make the gasket slide up to the groove. When the gasket temperature decreases, its diameter reduces accordingly and the gasket remains fitted in the groove and secured to the tubular assembly.
In a large turbomachinery, that may have a tubular assembly of a diameter well above 1.5 m and up to 2.8 m, a length of 2 m to 5 m, the closed-ring gasket destined to fit on it must have similar diameters. The huge dimension of the closed-ring gasket makes it difficult to increase its temperature in a homogenous way, and to handle it once heated (it must be noted that the heating temperature may be close to 100° C.).
The existing procedure provides for the operators to heat up the gasket using portable heaters, generating a stream of hot air that can warm up only on a limited portion of the gasket. Therefore, 3-4 operators need to act at the same time on the gasket in order to heat it in a substantially homogeneous way. During the procedure, every operator must be very careful in order to avoid overheating that may permanently deform some parts of the gasket, compromising the seal.
Once the gasket is heated to the correct temperature, the operators must position it on the tubular assembly and make it slide over the tubular assembly surface up to the correct position above the groove.
During this operation, the entire tubular assembly is usually positioned on two spaced-apart supports. Therefore, in order to position the gasket, the operators need to lift the tubular assembly at least from one support and fit the gasket on the assembly. After that, they need to make the gasket slide up to a position where it does not interfere with the support, and, once that position is reached, they can lower down the tubular assembly to its original place. The last step of the procedure provides to continue the sliding movement of the gasket until it reaches the final position.
The operation, that is already not easy, is complicated by the fact the temperature of the gasket is around 100° C. This requires the operators to wear suitable protections, in order to avoid severe burnings to the skin. Moreover, the operation needs to be completed as quickly as possible, in order to avoid a cooling of the gasket.
In fact, if the gasket temperature falls below a certain limit, while it is not yet in the correct position, it may remain blocked on the tubular assembly due to its diameter reduction, and it may be difficult to re-position it.
It is also to be noted that, in the prior art, once the gasket is positioned in the groove, it is very difficult to heat it up to the correct temperature in order to remove it. Therefore, most of the times, an installed gasket need to be destroyed and it cannot be re-used.